1. Field of the Invention
The present invention relates to a water jet propulsion watercraft including a jet unit (jet propulsion device) having an engine (internal combustion engine) as a drive source.
2. Description of Related Art
An example of a water jet propulsion watercraft is disclosed in U.S. Patent Application Publication No. 2004/0194682 A1. This water jet propulsion watercraft includes a hull, a water jet pump, and an engine. The engine applies a driving force to the water jet pump. The water jet pump includes a propeller shaft rotated by the driving force of the engine, and an impeller coupled to the propeller shaft. By rotation of the propeller shaft, water is sucked in from a hull bottom and the water is jetted rearward by the impeller. A propulsive force is thereby applied to the hull.
The engine has a crankcase at a lower side. A crankshaft housed in the crankcase is extended to a rear of the crankcase, and an extended axial member is coupled to a rear end of the crankshaft. The propeller shaft is coupled to the extended axial member via a coupling.
A housing is disposed at the rear of the crankcase. The crankshaft is coupled to the extended axial member inside the housing. A power generator, which is a heavy object, is disposed inside the housing. A center of gravity of the small planing watercraft can thus be positioned at the rear.
To dispose the power generator at the rear of the crankcase, a space for disposing the power generator has to be secured between the crankcase and the coupling. The extended axial member is disposed between the crankshaft and the coupling to secure this space.
More specifically, a rear end portion of the crankshaft has a tapered shape portion, at the rear of which a male screw is formed coaxial with a rotational center axis of the crankshaft. A female screw, engageable with the male screw, is formed at a front end portion of the extended axial member. During assembly, the female screw of the extended axial member is fastened to the male screw of the crankshaft with a rotor of the power generator being disposed at the tapered shape portion of the crankshaft. The rotor and the extended axial member are thereby fixed to the crankshaft.